The present invention relates to a room temperature curable silicone composition. More particularly, the present invention relates to a one-pack, room temperature moisture curable silicone composition.
Various silicone compositions capable of providing a rubber-like elastomer on curing at room temperature are known. Such silicone compositions comprising silanol-terminated polyorganosiloxanes are classified into two types, namely, one-pack type and two-pack type. For convenience of use and workability, the one-pack type silicone composition has been preferably used. It is known that the one-pack type silicone compositions include an acetic acid-evolving type, an alcohol-evolving type and an acetone-evolving type.
The one-pack type room temperature curable silicone composition is usually composed of a silanol-terminated polyorganosiloxane, a crosslinking agent comprising a polyfunctional compound capable of reacting with the silanol-terminated polyorganosiloxane and a curing agent capable of promoting the reaction of the silanol-terminated polyorganosiloxane with the crosslinking agent.
As the crosslinking agent, there are mentioned acyloxysilanes, alkoxysilanes, aminosilanes, isocyanatosilanes and the like. With respect to the curing agent, amines, metallic soaps, metal alkoxides and metal chelates are known. However, these one-pack type room temperature curable silicone compositions are generally unsatisfactory with regard to one or more characteristics among storage stability, curing rate, resultant resin properties, adhesive properties, workability and insusceptibility to discoloration. Particularly, most of these silicone compositions, except for the acetic acid-evolving type, are accompanied by a problem in that the curing is very slow. Also, those which exhibit a high curing rate are likely to violently corrode the surrounding materials and exhibit unsatisfactory adhesion. Therefore, there is still room for improvement.
In order to improve the curing rate and the adhesion of the above-mentioned silicone compositions, Japanese Patent Publication Nos. 3979/1968 and 14196/1970 have proposed a composition comprising a silanol-terminated organopolysiloxane, a crosslinking agent consisting of a monoorganosilylisocyanate and a curing agent selected from the group consisting of amines, metallic soaps and organotin derivatives. These compositions can be cured in a shorter period of time, i.e., about 20 minutes, as compared with the conventional one-pack type room temperature curable silicone compositions.
However, the compositions proposed by these patents are unsatisfactory in storage stability. For example, the composition comprising triethylamine as the curing agent can be stored for a period of about half year, but they become unstable if the storage is further continued. Also, the compositions comprising diamines, metallic soaps, or organotin derivatives exhibit poor storage stability as is readily understood from the fact that these compounds are usually used as a curing agent for a two-pack type room temperature curable composition.Therefore, such compositions are useless for practical purposes. Moreover, during or after the curing procedure, the compositions comprising triethylamine exhibiting fairly good storage stability liberate amines which may result in corrosion of the surrounding materials or give off an offensive odor.